1. Field of the Invention
The present invention relates to an oil storage structure for a small-sized vehicle engine, and to an engine and a vehicle incorporating the same. More particularly, the present invention relates to an oil storage structure including an oil storage chamber formed by a partition wall splitting a space between a crankcase and a crankcase cover of an engine, and to an engine and a vehicle incorporating the same.
2. Description of the Background Art
There are known conventional engines, in which a crankshaft chamber is isolated from a transmission chamber, and an oil pump (scavenging pump) is adapted to draw in oil from the oil pan, and to supply pressurized oil to the crankshaft chamber and the transmission chamber. Oil is stored in an oil pan disposed below the crankshaft chamber, and in the transmission chamber communicating with the oil pan. An example of such known arrangement of the transmission chamber and the clutch chamber is disclosed in the Japanese Patent No. 2578284, specifically in FIG. 8 thereof.
In such a known engine configuration, gears of a transmission unit (mechanism) do not dip into the oil. Therefore, the transmission chamber and the clutch chamber are allowed to communicate with each other, so that oil is also stored in the clutch chamber. Thus, the height of the oil can be suppressed to a lower level compared with the transmission chamber alone.
However, if the transmission chamber is allowed to communicate with the clutch chamber, as stated above, the lowest end of a clutch is usually located at a position lower than the transmission gears. This leads to a problem that the clutch dips into the oil. Under conditions where a portion of the clutch constantly dips into oil, oil-separation performance between clutch plates lowers, which problematically affects the disengagement performance of the clutch.
In order to solve such problem, there is a known engine, in which an oil storage chamber for storing oil therein is formed so as to avoid the outer circumference of a clutch. An example of such engine is disclosed in the Japanese Patent No. 3052002, specifically in FIG. 7 thereof (in which an oil tank is shown by reference numeral 51).
However, in the case where the oil storage chamber is formed so as to avoid the clutch, it is necessary to form a vertically long oil storage chamber for ensuring that a sufficient volume of oil is stored in the oil storage chamber.
In a conventional engine, since the crankcase is split into right and left crankcase halves, one of the right and left cases and a clutch cover can constitute the oil storage chamber. However, if such configuration is used for the crankcase formed in a vertically split manner, the oil storage chamber will be formed by the upper and lower crankcases and the clutch cover. If the oil storage chamber is formed so as to straddle the three components, e.g. the upper and lower crankcases and the clutch cover, as described above, there arises a problem in that it is difficult to ensure a well sealed liquid-tight performance of the oil storage chamber.
The present invention has been made to overcome such drawbacks of previously known configurations of the oil storage chamber. Accordingly, it is one of the objects of the present invention to provide an oil storage structure for an engine provided with a vertically split crankcase, in which a clutch mechanism does not dip into oil so as not to affect clutch disengagement performance.
It is another object of the present invention to provide an oil storage structure for an engine which is arranged so that liquid-tight sealing performance of the oil storage chamber is reliably ensured.